A note to my Yarns from the Farm Readers—this is the second instalment of a series on biodiversity for our local newspaper. The previous Yarn, Biodiversity, was the introduction. Nan
Biodiversity is not just a pretty face. It’s critical for nutrition for animals of all descriptions, including us.
All plants have developed chemical defences to keep from being overeaten. Known as secondary compounds, these are sophisticated chemicals like tannins and alkaloids. Oregano, for instance, a common culinary herb, boasts 26 different secondary compounds.
Secondary compounds do a couple of key things for us mammals. First, they limit how much we want to eat of a given plant, by making us faintly nauseous if we eat (or drink) too much of it. Think of the way your tummy feels after the 4th cup of tea or coffee, even SGC (seriously good coffee).
Your system learns to recognise the effect on your digestion of a given secondary compound, like tannin, and is able to autonomically connect that effect to the taste (actually smell) of the chemical involved. Over time we animals learn to limit the amount we eat based on past experience.
As an important aside, mammals have an amazing ability to distinguish different chemicals on the basis of smell, presumably because we have needed to do so to stay healthy. I’m reasonably sure that herbivores preferentially graze into the wind because they are sniffing out the secondary compounds they are after.
Secondary compounds are also pharmaceuticals—small pharma, if you like, rather than big pharma. The vast majority of medicines derive originally from plants. Until the last couple of centuries essentially all medication came by way of herbs and spices, plants unusually rich in secondary compounds.
If animals have enough plants to choose from, and are given the opportunity to learn the effects those plants have on their bodies, they will balance their diets and self-medicate through those choices. An example of self-medication might be eating willow leaves and twigs which contain salicylic acid, the active ingredient in aspirin.
We humans can also use secondary compounds to stay healthy, but a number of things get in our way. Sugar, for instance, provides calories with no secondary compounds whatsoever to help us limit our intake. Sugar throws the system out of whack.
What about carnivores? Well, carnivores eat the intestinal contents of the animals they kill, as well as the flesh and bones. The plant matter in the gut of a prey animal contains all the secondary compounds it has ingested. So predators depend on the good nutrition of herbivores to stay healthy themselves.
Which brings us back to the diversity of the environment. The higher the level of biodiversity, the more likely it is for all the herbivores in the system to find enough different secondary compounds to stay healthy by moving from plant to plant. This is not quite as easy as it sounds, if you stop and think about the complexity facing any individual herbivore in a diverse ecosystem.
In fact, mamas teach their babies where to find what they need, and how to know when to eat which plants. They do this by example, with the process of teaching babies to be nutritionally adapted to their local environment taking 2-3 years, a length of time that will come as no surprise to human mothers. For maximal livestock health, this means babies should stay with their mothers for several years to learn the secrets their mamas know.
Since 2008, I’ve kept lambs with their mothers for their lifetimes on the farm. I’ve also reduced grazing pressure by about a factor of three to enhance biodiversity: you can’t have biodiversity without abundance, because the animals will eat the biodiversity first. Among other benefits, like increased wool production and quality, my sheep have not needed treatment for intestinal parasites in the intervening 13 years. Additional reading: Fred Provenza, Nourishment, 2018 Chelsea Green Publishing; ISBN 9781603588027.